I heard "nonce" get used as a general insult when I was a kid and probably used it once or twice myself when younger - thinking it was along the lines of "nonse" being short for "nonsense" or something related to that. After finding out that it also meant paedo, I don't think I've heard anyone use it in any other context.

I know it means paedophile, but I've definitely heard it used in a way that isn't solely for accusing someone of that, in the same way a lot of swear words are. Like, you might tell someone to stop noncing about if they're acting a bit stupid.

I've definitely said nonce and not meant it as paedo, but that would have been before what it meant. Same with mong, I remember a period of school where we used to call each other things, that being one of them. Again, I don't remember it being anything other than just meaning someone was stupid (becuase we'd call each other it if we'd done something daft).